1. Field of the Invention
The present invention relates to a surge absorber used to protect various devices from surges and to avert accidents beforehand, and to a production method thereof.
2. Description of the Related Art
Surge absorbers are connected to parts that can easily receive electric shocks due to abnormal voltages (surge voltage) from lightning surges and static electricity, such as CRT driving circuits, and the communication lines and connections of electronic devices for use in telecommunication equipment such as telephones, facsimiles, and modems, in order to prevent thermal damage or ignition due to abnormal voltages, of the printed board on which the electrical devices and their equipment are mounted.
Heretofore, a surge absorber using a microgap surge absorber element, such as disclosed for example Japanese Unexamined Patent Application, First Publication No. Hei 7-320845, has been proposed. This surge absorber is one where, in an electric discharge surge absorber where a surge absorber element with a pair of cap electrodes provided on opposite ends of a ceramics member encapsulated by a conductive film and with a so-called microgap formed on a peripheral surface thereof is accommodated inside a glass tube together with an inert gas, as shown in FIG. 11, the opposite ends of a glass tube 1 are sealed by bonding a pair of sealing electrodes 2 by high temperature heating. This surge absorber is a surface mount type (melph type) surge absorber. There are no lead wires in the sealing electrodes 2, and when mounting, this is connected and secured by soldering the sealing electrodes 2 to a substrate.
As illustrated in FIG. 12, this kind of surge absorber is made by inserting one sealing electrode 2, a glass tube 1, a surge absorber element 4, and then the other sealing electrode 2 in this order into a hole portion 10a formed in a carbon heater jig 10, and then after replacing the interior with an inert gas, heating the carbon heater jig 10 under a condition with a pressure applied axially, so that the opposite ends of the glass tube 1 are sealed by the pair of sealing electrodes 2.
However, for the above-mentioned conventional surge absorber, the following problems remain. That is, in this surge absorber, when the surge absorber element is inserted into the hole of the carbon heater jig during production, the surge absorber element leans to one side, resulting in a situation where the central axis of the surge absorber element is misaligned to the central axis of the glass tube. When the surge absorber element is sealed in this misaligned condition, the surge absorber element touches the glass tube, so that at the time of discharge, the conductive film disintegrates and is easily adhered to the glass tube, resulting in a situation where the life span of the surge absorber element and the surge current capacity is lowered. In addition, because the electrodes are installed into both ends, the surge absorber element has a high cost. Moreover, the surge absorber is lengthened by an amount of the electrodes.
Furthermore, in this surge absorber, because an easily acquired and inexpensive cylindrical glass tube is used, this rolls easily when mounted on a flat substrate or the like, and cannot be secured in position unless secured with an adhesive or metal fitting. Hence there is a deficiency in work efficiency at the time of mounting.
The present invention take the above problems into consideration, with a first object being to provide a surge absorber and a production method therefor whereby the surge absorber element can be positioned in the center of the glass tube with high accuracy, the life span and the surge current capacity of the surge absorber can be improved, and low cost and small size can be achieved. Moreover, a second aim is to provide a surge absorber with superior installation work efficiency, that does not roll easily.
A first aspect of the present invention relates to a surge absorber provided with; a surge absorber element composed of a columnar non-conductive member and a conductive film formed dividedly via a discharge gap on a peripheral surface of the nonconductive member, a pair of sealing electrodes disposed at opposite ends of the surge absorber element and touching the conductive film, and a glass tube with opposite ends closed by the pair of sealing electrodes and the surge absorber element and an inert gas encapsulated thereinside, and is characterized in that a face of each sealing electrode which contacts with the surge absorber element is formed in a concave shape symmetrical with a central axis of the glass tube.
A second aspect of the present invention relates to a production method for a surge absorber provided with; a surge absorber element composed of a columnar nonconductive member and a conductive film formed dividedly via a discharge gap on a peripheral surface of the non-conductive member, a pair of sealing electrodes disposed at opposite ends of the surge absorber element and touching the conductive film, and a glass tube with opposite ends closed by the pair of sealing electrodes and the surge absorber element and an inert gas encapsulated thereinside. The production method is characterized in having; an insertion step for inserting one of the pair of sealing electrodes, the glass tube, the surge absorber element, and the other of the pair of sealing electrodes in this order into a hole formed in a production jig of an internal diameter into which the glass tube can be inserted; and a welding step involving replacing an atmosphere gas inside the hole with an inert gas and then welding the sealing electrodes to the glass tube inside the hole by heating the production jig, and a face of each sealing electrodes inserted in the insertion step which contacts with the surge absorber element is formed in a concave shape symmetrical with a central axis of the glass tube which is inserted.
A third aspect of the present invention relates to a surge absorber provided with; a surge absorber element composed of a columnar non-conductive member and a conductive film formed dividedly via a discharge gap on a peripheral surface of the non-conductive member, a pair of sealing electrodes disposed at opposite ends of the surge absorber element and touching the conductive film, and a glass tube with opposite ends closed by the pair of sealing electrodes and the surge absorber element and an inert gas encapsulated thereinside, and is characterized in that a flat portion is formed on at least one portion of an outer peripheral surface of the glass tube.
In this case, preferably at least a pair of the flat surfaces are formed in parallel on opposite sides of the glass tube. Moreover, more preferably a transverse section of the glass tube is a square shape touching an outer periphery of the pair of sealing electrodes.
Furthermore, preferably a ratio of a transverse section area of the surge absorber element to a transverse section area of an inner space of the glass tube is from 1:3 to 1:15.